ArF photoresist copolymers

ABSTRACT

A photoresist copolymer is prepared from one or more carboxy-substituted bicycloalkene monomers, and this copolymer is used to prepare a photoresist for submicrolithography processes employing deep ultraviolet (ArF) as a light source. In addition to having high etch resistance and thermal resistance, the photoresist has good adhesiveness to the substrate and can be developed in a TMAH solution.

CROSS-REFERENCES TO RELATED APPLICATIONS

This is a continuation-in-part of application Ser. No. 09/000,984, fled Dec. 30, 1997, now U.S. Pat. No. 6,132,926.

BACKGROUND OF THE INVENTION

1.Field of the Invention

The present invention relates to the fabricating of an integrated circuit. More particularly, the invention provides an ArF photoresist resin and a preparation method therefor and, more particularly, to a photoresist copolymer suitable for submicrolithography using deep ultra violet (DUV) light as a light source and a method for preparing such a copolymer. Also, the present invention provides a photoresist composition (“photoresist”) including such a resin.

2. Description of the Prior Art

Recently, chemical amplification photoresists have been prevailing in semiconductor devices since they have been found to be highly sensitive to DUV light, which is recognized as a light source suitable for accomplishing the high integration of semiconductor devices. A chemical amplification photoresist generally has a photoacid generator and a matrix polymer having a chemical structure which sensitively reacts with acid.

As for the reaction mechanism of such a photoresist, when the photoresist is exposed through a mask to a DUV light source, protons are generated by the action of the photoacid generator, which then reacts with the main or side chain of the matrix polymer. This reaction increases the solubility of the copolymer in a developing solution by converting the structure of the copolymer, e.g., by decomposing it, cross-linking it or changing its polarity. Therefore, when treated with the developing solution, the copolymer is dissolved at exposed regions and remains undissolved at unexposed regions, thereby leaving the shape of the mask as a positive image on a substrate.

Meanwhile the resolution of the patterns formed by photolithography is generally proportional to the wavelength of the light source. Thus, finer patterns can be formed as the wavelength is shorter. As a result of the effort to find new light sources suitable to improve the resolution, deep UV (DUV) light was developed for the integration of semiconductor devices into 1 Giga or higher scale.

Generally, photoresists are required to be of high etch resistance and thermal resistance. In addition, the photoresist to be used for an ArF (193 nm wavelength) light source should be developed in a 2.38% tetramethylammonium hydroxide (TMAH) solution. However, in fact, it is difficult to obtain a photoresist resin which satisfies those properties entirely.

For example, resins having a backbone of poly(methylmethacrylate), which is transparent to light of the above short wavelengths, are easy to synthesize. But there are problems in practical application owing to their poor etch resistance and development in TMAH solution. Etch resistance can be improved by introducing aliphatic ring monomers into the main chain. But it is virtually impossible to synthesize a resin having a main chain consisting of aliphatic rings.

In order to solve the problems, people such as those at AT&T (or Bell Laboratory) has developed a resin having a main chain which comprises norbornene, acrylate and maleic anhydride monomers, as represented by the following formula I:

In Formula I, the maleic anhydride (part A) is used to polymerize aliphatic cyclo-olefin groups, but is dissolved in a 2.38% TMAH solution even in the state of unexposure. This dissolution can be inhibited by increasing the proportion of the y part of Formula I, the t-butyl substituent, in the main chain. If this is done, the z part, functioning to increase the adhesiveness to a substrate becomes relatively small in proportion, which leads to the release of the photoresist from the substrate, e.g. a silicon wafer. As a result, the formation of good patterns is impossible by this method. Bell Laboratory suggested a two-component system including a cholesterol compound as a dissolution inhibitor. This dissolution inhibitor is, however, required to be added in a large quantity, for example, about 30% by weight of the resin, so that Bell Laboratory's resins are in principle problematic for use in a photoresist.

SUMMARY OF THE INVENTION

Therefore, it is an object of the present invention to overcome the above problems encountered in prior art and to provide an ArF photoresist resin which is dissolved only slightly in developing solutions without a chemical change in its structure in addition to being superior in etch resistance, thermal resistance and adhesiveness.

It is an object of the present invention to provide a photoresist copolymer.

It is another object of the present invention to provide a method for preparing the photoresist copolymer.

It is a further object of the present invention to provide a photoresist comprising the photoresist copolymer.

It is still another object of the present invention to provide a method for fabricating the photoresist.

It is still another object of the present invention to provide a method for fabricating an integrated circuit device.

It is still another object of the present invention to provide a partially complete semiconductor device.

DETAILED DESCRIPTION OF THE INVENTION

The novel photoresist copolymers of the present invention comprise repeating units in the backbone of the polymer derived from one or more carboxy- substituted bicycloalkene monomers of the following Formula II:

wherein, R represents hydrogen or a straight or branched alkyl group containing 1-10 substituted or non-substituted carbon atoms, R of one of said bicycloalkenes being hydroxyalkyl; and n is 1 or 2. As shown in Formula II, the monomers of the present invention are polymerized through the double bond in the bicycloalkene ring.

In Formula II, preferred R groups are hydrogen, 2-hydroxyethyl and t-butyl That is, preferred examples of the bicyclocalkene monomers include 2-hydroxethyl 5-norbornene-2-carboxylate, t-butyl 5-norbornene-2-carboxylate, 5-norbornene 2-carboxylic acid, 2-hydroxyethyl bicyclo [2,2,2] oct-5-ene-2-carboxylate, t-butyl bicyclo [2,2,2] oct-5-ene-2-carboxylate and/or bicyclo [2,2,2] oct-5-ene-2-carboxylic acid.

The copolymer of the invention has a molecular weight ranging from approximately 3,000 to 100,000.

Preferred polymers of Formula 11 comprise at least two carboxy-substituted bicycloalkene monomers and are represented by the following Formula II:

wherein R₁ is hydroxyalkyl; R₂ is hydrogen or alkyl; n is 1 or 2; and x and y represent the relative amounts of each monomer. Preferably, for every monomer represented by x, there are two monomers represented by y, wherein R₂ is hydrogen in one of said y monomers and R₂ is t-butyl in the other y monomer.

Hydroxyalkyl groups represented by R₁ in Formula IIA may have from 1 to 10 carbon atoms, preferably from 1 to 6 carbon atoms, and most preferably from 1 to 4 carbon atoms. Examples of preferred hydroxalkly groups are 2-hydroxyethyl, 2-hydroxy propyl, 3-hydroxy propyl, 2- hydroxy butyl, 3-hydroxy butyl, 4-hydroxy butyl and 2-methyl-3-hydroxy propyl.

Alkyl groups represented by R₂ in Formula IIA are preferably blocking or protective groups that are clearable by acid generated by the photoacid generator used in the photoresist composition. A preferred alkyl group is t-butyl.

The copolymers of the present invention may be prepared by polymerization with only the alicyclic compounds represented by Formula II using known polymerization methods, for example using a metal catalyst system as described in Goodall et al, International Publication Number WO 96/37526. However, the preferred polymerization method for the practice of the present invention is to incorporate one or more additional monomers (hereinafter referred to as the polymerization-enhancing comonomers) to increase the yield of copolymer. The most preferred polymerization-enhancing comonomers are maleic anhydride, having the following Formula III:

and/or vinylene carbonate of the following Formula IV:

One of the preferred copolymers of the invention is prepared from vinylene carbonate and three bicycloalkenes wherein R in Formula II is hydrogen, 2-hydroxy ethyl and t-butyl, respectively, and n is 1. That is, in a preferred embodiment the three bicycloalkene monomers are 2-hydroxyethyl 5-norbornene-2-carboxylate, t-butyl 5-norbornene-2-carboxylate and 5-norbornene 2-carboxylic acid.

Preferred copolymers of the present invention may be prepared according to ordinary radical polymerization techniques using radical polymerization initiators in bulk polymerization or in solution polymerization processes. For the polymerization solvent, cyclohexanone, methylethylketone, benzene, toluene, dioxane, dimnethylformamide, and tetrahydrofuran alone, or combinations thereof, may be used. Usually, the polymerization is carried out in the presence of a polymerization initiator, such as benzoylperoxide, 2,2′-azobisisobutyronitrile (AIBN), actyl peroxide, lauryl peroxide and t-butylperacetate.

A positive photoresist composition useful for forming positive fine patterns in semiconductor devices may be obtained by mixing the novel photoresist copolymer of the invention with a photoacid generator in an organic solvent in a typical manner. The amount of the copolymer is dependent on the organic solvent, the photoacid generator and the lithography conditions, and is preferably about 10-30% by weight of the organic solvent used.

As an example of a method of fabricating a photoresist, the copolymer of the invention is first dissolved in cyclohexanone at an amount of 10-30% by weight and an onium salt or organic sulfonic acid, as a photoacid generator, is added at an amount of about 0.1-10% by weight of the photoresist polymer. Then, this solution is filtered with an ultra fine filter to yield a photoresist solution.

This photoresist solution is spin-coated on a silicon wafer and is, then, soft-baked at a temperature of 80-150° C. for 1-5 min. in an oven or on a hot plate. An exposure process is carried out by use of a stepper which employs DUV light or excimer laser as a light source. Thereafter, the wafer is subjected to post-baking at a temperature of 100-200° C. An ultrafine positive resist image can be obtained by immersing the post-baked wafer for 90 seconds in a 2.38% TMAH solution.

A better understanding of the present invention may be obtained in light of following examples which are set forth to illustrate, but are not to be construed to limit, the present invention.

EXAMPLE I Synthesis of 2-hydroxyethyl 5-norbornene-2-carboxylate

Dicyclopentadiene of the following formula V was cracked at about 120-170° C., thereby obtaining cyclopentadiene of the following Formula VI.

Cyclopentadiene of Formula VI and 2-hydroxyethylacrylate of the following Formula VII are dissolved at the same rate in ether or tetrahydrofuran and reacted at a temperature of about −30 to 60° C. for 24 hours. Thereafter, the solvent is removed by use of a rotary evaporator and the residue is distilled in vacuo to give 2-hydroxyethyl 5-norbornene-2-carboxylate of the following Formula VIII, which occurs in an endo- and exo-mixture.

EXAMPLE II Synthesis of t-butyl 5-norbornene-2-carboxylate

66 g of cyclopentadiene is first put in a reactor and then mixed with 500 g of tetrahydrofuran. 128 g of t-butyl acrylate is added to the reactor. Thereafter, these reactants are subjected to a reaction at a temperature of −30 to 60° C. for 10 hrs with stirring. After the completion of the reaction, the solvent is vaporized in vacuo by use of a rotary evaporator, then vacuum distilled to produce the subject compound: yield is 90%.

EXAMPLE III Synthesis of Copolymer

91 g of the 2-hydroxyethyl 5-norbornene-2-carboxylate synthesized in Example I, 97 g of the t-butyl 5-norbornene-2-carboxylate synthesized in Example II, and 86 g of vinylene carbonate are put into a reactor and 182 g of tetrahydrofuran solvent is poured thereto. Then, 5.48 g of azobisisobutyronitrile (AIBN) is added into the reactor. Then, the reactor is purged with a nitrogen atmosphere. A reaction is performed for 6 hrs. at 65-120° C. After the completion of the reaction, a part of the solvent is removed by a rotary evaporator and the residue is precipitated in ethyl ether. The precipitate is filtered and dried in a vacuum oven. The resulting product can be used as a photoresist resin.

EXAMPLE IV Synthesis of Copolymer

91 g of the 2-hydroxyethyl 5-norbornene-2-carboxylate synthesized in Example 1, 97 g of the t-butyl 5-norbornene-2-carboxylate synthesized in Example II, and 98 g of maleic anhydride are put in a reactor and 190 g of tetrahydrofuran solvent is poured thereto. Then, 5.72 g of azobisisobutyronitrile (AIBN) is added into the reactor. Then, the reactor is purged with a nitrogen atmosphere. A reaction is performed for 6 hrs. at 65-120° C. After the completion of the reaction, a part of the solvent is removed by a rotary evaporator and the residue is precipitated in ethyl ether. The precipitate is filtered and dried in a vacuum oven. The resulting product can be used as a photoresist resin.

EXAMPLE V Synthesis of Copolymer

98 g of 2-hydroxyethyl bicyclo [2,2,2] oct-5-ene- 2-carboxylate, 104 g of t-butyl bicyclo [2,2,2] oct-5-ene-2-carboxylate and 86 g of vinylene carbonate are put into a reactor and then, mixed with 2 L of tetrahydrofuran solvent. Thereafter, 1.5 g of azobisisobutyronitrile (AIBN) is put into the reactor and then the reactor is purged with a nitrogen atmosphere. A reaction is performed for 6 hrs. at 65° C. After the completion of the reaction, a part of the solvent is removed by a rotary evaporator and the residue is precipitated in ethyl ether. The precipitate is filtered and dried in a vacuum oven. The resulting product can be used as a photoresist resin.

EXAMPLE VI Synthesis of Copolymer

98 g of 2-hydroxyethyl bicyclo [2,2,2] oct-5-ene-2-carboxylate, 104 g of t-butyl bicyclo [2,2,2] oct-5-ene-2-carboxylate and 86 g of 98 g of maleic anhydride are put into a reactor and then, mixed with 2 L of tetrahydrofuran solvent. Thereafter 1.5 g of azobisisobutyronitrile (AIBN) is put into the reactor and then, the reactor is purged with a nitrogen atmosphere. A reaction is performed for 6 hrs. at 65° C. After the completion of the reaction, a part of the solvent is removed by a rotary evaporator and the residue is precipitated in ethyl ether. The precipitate is filtered and dried in a vacuum oven. The resulting product can be used as a photoresist resin.

EXAMPLE VII Synthesis of Copolymer Using Metal Catalyst

It is contemplated that the copolymers of Examples III-VI above may be polymerized without maleic an hydride or vinylene carbonate monomers, for example by using the allylpalladium chloride dimer/silver hexafluoroantimonate catalyst system described in Goodall et al. International Publication WO 96/37526. In accordance with, for example, Example 30 of Goodall et al., 37.5 mmol of t-butyl 5-norbornene-2-carboxylate and 12.5 mmol of 2-hydroxyethyl 5-norbornene-2-arboxylate and 50 mol of freshly distilled dichloroethane are added to a 50 ml glass vial equipped with a Teflon® coated stir bar and the solution is degassed under argon atmosphere. A 10 ml glass vial equipped with a Teflon® coated stir bar is charged with 0.0365 g (0.1 mmol) of allylpalladium chloride dimer (to ultimately give a monomer to catalyst ratio of 500/1) and 2 ml of dichloroethane. Another 10 ml glass vial is charged with 0.0344 g (0.1 mmol) of silver hexafluoroantimonate and 2 ml of dichloroethane. The catalyst solution is prepared by mixing the allylpalladium chloride dimer solution with silver hexaflurorantimonate solution inside a dry box. Immediate precipitation of silver chloride occurs and the precipitate is filtered out to obtain a clear yellow solution. The active yellow catalyst solution is added to the monomer solution via a syringe and the reaction mixture is allowed to stir for 20 hours at 60° C. Solids are precipitated from the solution, the solution is cooled, concentrated in a rotovap, and precipitated into hexane to obtain the polymer. The polymer is then dried in vacuum at room temperature.

EXAMPLE VIII Synthesis of Preferred ArF Photoresist Resin

Synthesis of poly [2-hydroxyethyl 5-norbornene-2carboxylate/t-butyl 5-norbornene-2-carboxylate/5-norbornene 2-carboxylic acid/maleic anhydride]

1 mole of maleic anhydride, 0.05-0.8 moles of 2-hydroxyethyl 5-norbornene-2-carboxylate, 0.5-0.95-moles of t-butyl 5-norbornene-2-carboxylate and 0.01 to 0.2 moles of 5-norbornene 2-carboxylic acid are dissolved in tetrahydrofuran or toluene. A radical reaction is executed at a temperature of about 60-70° C. for 4-24 hours under a nitrogen or argon atmosphere in the presence of 0.5-10 g of azobisisobutyronitrile (AIBN), as an initiator. The resin thus produced by this polymerization is precipitated in ethyl ether or hexane and dried to yield poly [2-hydroxyethyl 5-norbornene-2-carboxylate/t-butyl 5-norbornene-2-carboxylate/5-norbornene 2-carboxylic acid/maleic anhydride] resin of the following Formula X.

EXAMPLE IX Preparation of Photoresist Film and Formation of Pattern

10 g of poly [2-hydroxyethyl 5-norbornene-2-carboxylate/t-butyl 5-norbornene-2-carboxylate/1 5-norbornene 2-carboxylic acid/maleic anhydride] are dissolved in 40 g of 3-methoxymethyl propionate solvent and added with about 0.02.-1 g of triphenyl sulfonium triflate or dibutylnaphthyl sulfonium triflate or mixture of these two photoacid generators. After being well stirred, the mixture is passed through a 0.10 μm filter. This filtrate is coated on a wafer and patterned. When the coated layer is about 0.6 μm thick, a vertical L/S pattern is obtained with resolution of 0.14 μm.

As described hereinbefore, the photoresist prepared from the novel copolymer of the invention is superior in etch resistance and thermal resistance. In addition, it can be developed in a 2.38% TMAH solution. It also shows such good adhesiveness that 0.15 μm L/S patterns with satisfactory resolution and depth of focus can be obtained from a photoresist coat 0.7 μm thick. Consequently, the introduction of, for example, 2-hydroxyethyl 5-norbornene-2-carboxylate into the backbone of a resin allows for a synthesis of a photoresist excellent in adhesiveness.

The present invention has been described in an illustrative manner, and it is to be understood the terminology used is intended to be in the nature of description rather than of limitation.

Many modifications and variations of the present invention are possible in light of the above teachings. Therefore, it is to be understood that within the scope of the appended claims, the invention may be practiced otherwise than as specifically described. 

We claim:
 1. A photoresist copolymer consisting of: two or more carboxy-substituted bicycloalkene monomers of the following Formula II:

wherein each R is independently hydrogen or a substituted or non-substituted C₁-C₁₀ straight or branched alkyl, provided R of at least one of said carboxy-substituted bicycloalkene monomer is C₁-C₁₀ hydroxyalkyl; and n is 1 or
 2. 2. A photoresist copolymer in accordance with claim 1 wherein said hydroxyalkyl contains from 1 to 4 carbon atoms.
 3. A photoresist copolymer in accordance with claim 2 wherein said hydroxyalkyl is 2- hydroxyethyl.
 4. A photoresist copolymer in accordance with claim 1 wherein R of at least one of the other carboxy-substituted bicycloalkene monomer is t-butyl.
 5. A photoresist copolymer in accordance with claim 1 wherein R of at least one of the other carboxy-substituted bicycloalkene monomer is hydrogen.
 6. A photoresist copolymer in accordance with claim 1, wherein one of said carboxy-substituted bicycloalkene monomer is selected from the group consisting of 2-hydroxyethyl 5-norbornene-2-carboxylate and 2-hydroxyethyl bicyclo (2,2,2) oct-5-ene-2-arboxylate, and the remaining carboxy-substituted bicycloalkenes monomers are selected from the group consisting of t-butyl 5-norbornene-2-carboxylate, 5-norbornene 2-carboxylic acid, t-butyl bicyclo (2,2,2) oct-5-ene-2-carboxylate and bicyclo (2,2,2) oct-5-ene-2-arboxylic acid.
 7. A photoresist copolymer in accordance with claim 1, wherein said photoresist copolymer is derived from a mixture of said carboxy-substituted monomers comprising: (i) the compound of Formula II wherein R is C₁-C₁₀ alkyl; (ii) the compound of Formula II wherein R is C₁-C₁₀ hydroxyalkyl; and (iii) the compound of Formula II wherein R is hydrogen.
 8. A photoresist copolymer in accordance with claim 1, wherein the molecular weight of said photoresist copolymer is in the range of from about 3,000 to 100,000.
 9. A photoresist composition comprising a copolymer of claim 1, a photoacid generator and an organic solvent.
 10. A photoresist composition in accordance with claim 9 wherein said photoacid generator is an onium salt or organic sulfonic acid.
 11. A photoresist-composition in accordance with claim 10 wherein said photoacid generator is triphenyl sulfonium triflate or dibutylnaphthyl sulfonium triflate, or a mixture thereof.
 12. A semiconductor device comprising a substrate and a film of the photoresist composition of claim 9 overlying said substrate.
 13. A method of preparing the copolymer of claim 1 which comprises polymerizing said bicycloalkene monomers using a metal catalyst system.
 14. The method in accordance with claim 13 wherein said metal catalyst system comprises allylpalladium chloride dimer and silver hexafluoroantimonate.
 15. A photoresist copolymer having the following Formula IIA:

wherein R₁ is hydroxyalkyl; R₂ is hydrogen or alkyl; n is 1 or 2; and x and y represent the relative amounts of each monomer.
 16. A photoresist copolymer in accordance with claim 15 wherein the ratio of x:y is 1:2 and a portion of R₂ is hydrogen and the remainder of R₂ is t-butyl. 